If your rear crankshaft seal is leaking, it is very likely that the old hardened seal rubber can no longer seal effectively against the surface of the rear crankshaft flange. One of the primary reasons, in addition to the old seal, is that there is a groove worn into the crankshaft surface.

The Speedi-Sleeve is a precision machined, ultra thin stainless steel sleeve that is a press fit over the worn surface. The sleeve is thin enough that it doesn't impact the operation of a new seal, and it the sleeve provides a brand new sealing surface.